The use of plastic housings for electronic equipment and components is widely accepted in the automotive and electronic equipment fields today. However, the presently available plastic materials suffer from the disadvantage of being transparent or permeable to electromagnetic interference commonly known as, and referred to, as EMI. This drawback in available plastic materials is a matter of considerable concern in view of the susceptibility of electronic equipment to the adverse effects of EMI emission by the growing number of consumer products which produce such EMI signals, and to the increasing regulatory controls exercised over such electromagnetic pollution.
Currently, the major approach to solving plastic material shielding problems is through the application of metallic surface coatings to the molded plastic. Among such approaches are the use of vacuum deposition, metal foil linings, metal-filled spray coatings, zinc flame-spray and electric arc discharge. Each of these procedures is accompanied by one or more drawbacks with respect to cost, adhesion, scratch resistance, environmental resistance, the length of time required for application and the difficulties in adequately protecting many of the adverse geometrical forms in which the molded plastic must be provided.
More recently, attempts have been made to resolve the problem of EMI by formulation of composite plastic materials based upon the use of various fillers in thermoplastic matrices. However, none of the composite plastic products developed heretofore have proven completely satisfactory.
It is further noted that the addition of glass fibers and carbon fibers separately to resinous materials for the improvement of mechanical and physical properties is known in the field of reinforced plastic materials. Glass fibers have also been employed in compositions used in electrical applications, such as insulating enamels for electrical conductors. However, the use of glass fibers in such applications has been for the provision of physical properties such as resistance to plastic flow and to prevent abrasion of the enamel.